Cria (Cria cuervos; The Secret of Anna) (1976) [Ana, the Mother]: Dies (off-screen) of cancer, some time before the movie begins; she only appears in flashbacks and as a ghost or imaginary figure to her daughter (Ana Torrent). (Thanks to Constantine)

L'Adoption (1978) [Catherine]: Strangled by her adopted son (Patrick Norbert). (Thanks to The Midnight Club)

The House of Mirth(1981) [Lily Bart]: Presumably commits suicide by an overdose of laudanum. (I haven't seen this version, but I have seen Gillian Anderson's death in the 2000 version.)

Chaplin(1992) [Hannah Chaplin]: Dies (off-screen) of natural causes in 1928; I can't recall whether her death is mentioned specifically, but it did occur during the timeframe shown in the movie. (Thanks to Neil)

Cousin Bette (1998) [Adeline Hulot]: Dies off-screen of an unspecified terminal illness. She is shown on her deathbed in the opening scene, then the film cuts to her funeral during the credits (but neither her death nor her body is actually shown).